Biocompatible hydrogels for cartilage repair or as interpositional devices require mechanical integrity, high water content, and excellent lubricity to fully function under the high stress environment in the human joint spaces. PVA hydrogels are good candidates for such purposes, but currently available formulations do not provide enough mechanical strength, creep resistance, and lubricity compatible to that of natural articular cartilage.
Most hydrogels systems available for articular cartilage repair or replacement applications do not have required mechanical strength to withstand the high loads of the human joint. Various dehydration methods, described below, can be used together in combinations to alter the properties of hydrogels.
Solvent dehydration of hydrogels is described by Bao (U.S. Pat. No. 5,705,780). Bao describes immersion of PVA hydrogel into solvents such as ethanol/water mixture at room temperature to dehydrate PVA hydrogel without shape distortion.
Hyon and Ikada (U.S. Pat. No. 4,663,358) and Bao (U.S. Pat. No. 5,705,780) describe the use of water and organic solvent mixture to dissolve PVA powder and subsequently cooling the solution below room temperature and heating back up to room temperature to form a hydrogel. The hydrogel is then immersed in water to remove the organic solvent. Hyon and Ikada claim that PVA hydrogels thus formed are transparent, as opposed to the ones formed by freeze-thaw method that uses water only as the solvent to dissolve the PVA powder.
Bao (U.S. Pat. No. 5,522,898) describes dehydration methods that use air dehydration, vacuum dehydration, or partial humidity dehydration to control the rate of dehydration and prevent shape distortion of PVA hydrogels for use as prosthetic spinal devices to replace the nucleus pulposus. The starting gels of Bao are the freeze-thaw gels described in the U.S. Pat. No. 5,705,780.
Ku et al. (U.S. Pat. No. 5,981,826) describes a freeze-thaw method to form a PVA hydrogel by subjecting a PVA aqueous solution to freeze-thaw followed by immersion in water and additional cycles of freeze-thaw while immersed in water.
The creep resistance of PVA is currently achieved in the field by reducing the equilibrium water content (EWC) of the hydrogel, which also reduces the lubricity of the hydrogel. Therefore, there remains long felt but an unmet needs for a creep resistant, lubricious and tough PVA-hydrogel, which also would retain the lubricity. Such creep resistant, lubricious and tough PVA-PAAm-hydrogels and methods of making such compositions were not known until the instant invention.